Neuroplasticity is the brain’s ability to change under the influence of experience and activities. Several aspects of neuroplasticity are noteworthy: neurogenesis (development of new nerve cells) and synaptogenesis (development of new contacts between nerve cells) among them. Neuroplasticity used to be thought of as a limited phenomenon, mostly restricted to the early years of life. More recently it has been demonstrated that neuroplasticity continues throughout life, even in advanced age. This provides the conceptual basis for a wide range of therapeutic efforts aiming to slow the detrimental effects of aging on the brain and to treat various brain disorders.
What are the factors influencing neuroplasticity? The question is compelling both as a scientific challenge and because of the therapeutic promise of neuroplasticity once we know how to control and harness it. Among such factors, the environmental factors influencing neuroplasticity are particularly intriguing. It turns out that a strong relationship exists between what people do with their brains and how their brains age.
Both anecdotal observations and formal research suggest that education confers a protective effect against dementia. Highly educated people are less likely to succumb to its effects. Robert Katzman was the first to note that the prevalence of dementia, including Alzheimer’s disease, is lower in people with advanced education. The MacArthur Foundation Research Network on Successful Aging sponsored a study of the predictors of cognitive change in older persons. Education emerged as by far the most powerful predictor of cognitive vigor in old age.
The basis for this relationship is not fully understood. Does the lifestyle associated with education protect against dementia, or is it that some people are born with a particularly robust neurobiology that makes them better candidates for advanced education and protects them against dementia?
It is reasonable to assume that it is the nature of activities associated with advanced education that protects against dementia, rather than education itself. Highly educated people are more likely to engage in lifelong vigorous mental activities than less-educated people due to the sheer nature of their occupations.
Assuming that neurological dementia-causing illness strikes both groups with equal frequency, then equally severe neurological illness will have a less disruptive effect on the well-conditioned brain than on the poorly conditioned brain, because of the extra reserve that the well-conditioned brain has by way of additional neural connections and blood vessels. Equal amounts of structural damage will produce less functional disruption.
Again, the analogy between cognitive conditioning and physical conditioning comes to mind. The case of Sister Mary, discussed below, makes the point with dramatic and remarkable clarity. She performed well on cognitive tests until her death at the age of 101, despite the fact that the postmortem study of her brain revealed multiple neurofibrillary tangles and plaques, the hallmarks of Alzheimer’s disease. It would appear that Sister Mary had an intact mind inside an Alzheimer’s brain.
Sister Mary was one of the School Sisters of Notre Dame, the much-studied nuns from Mankato, Minnesota. Remarkable for their longevity, they were also known for the absence of debilitating dementia among them. The phenomenon was unanimously attributed to the lifelong habit of being cognitively active. The nuns constantly challenged their minds with puzzles, card games, debates of current policy issues, and other mental activities.
Furthermore, the nuns with college degrees, who taught and engaged in other mind-challenging activities on a systematic basis, on average lived longer than their less-well-educated counterparts. So compelling were the observations of the nuns’ cognitive well-being that a postmortem brain study was designed to examine the relationship between cognitive stimulation and dendritic sprouting.
In the nuns, the protective effect of cognitive exercise on the brain appeared to be cumulative, extending over the whole life span. Old convent records were found, containing the nuns’ autobiographies written when they were in their 20s. When the relationship between the nuns’ early life writings and the prevalence of dementia in later years was examined, a striking picture emerged. Those nuns who tended to write more grammatically complex and conceptually rich essays in their youth retained their mental vigor
These findings prompted speculation in the popular press that dementia is a lifelong process that begins to subclinically affect some people early in life, causing them to write simpler prose. But it is just as likely that the aspects of brain organization that make some people “smarter” than others also confer a protective effect against later-life dementia. Then again, it is also possible that the nuns who developed the habit of taxing their minds early in life, and presumably kept doing this, acquired the protective effect on the brain that proved to be of critical importance in their advanced years.
Data are rapidly accumulating that suggest that the effect of experience may actually change brain morphology even at a macroscopic level discernable on MRI.
